1. Field of the Invention
The present invention relates to a diagnostic method for diagnosing an electrochemical sensor provided with a solid or liquid electrolyte between a sensing electrode for contacting a gas to be detected and an opposite electrode and designed for detecting the concentration of the gas to be detected on the basis of a current flowing between the sensing electrode and the opposite electrode or a voltage corresponding to this current, and to an electrochemical sensor diagnostic apparatus.
2. Description of the Related Art
An electrochemical sensor usually comprises a sensing electrode and an opposite electrode having an electrolyte solution or a solid electrolyte in between, and is configured to enable detection of the concentration of a gas to be detected in accordance with an output of a current generated by the sensing electrode oxidizing the gas to be detected or a voltage corresponding to this current (hereafter sometimes simply called current for short). An example of this electrochemical sensor is a CO sensor for detecting carbon monoxide gas or the like as the gas to be detected.
Such an electrochemical sensor is mounted, for example, in an alarm apparatus or the like demanding high reliability, and it thus of great necessity that concentration detection always functions correctly. Specifically, it would be desirable to diagnose whether or not concentration detection in an electrochemical sensor is functioning correctly, and to continue to use the electrochemical sensor when it is functioning correctly and immediately stop use and initiate a replacement procedure when it is not functioning correctly or there is a warning sign that not functioning correctly is imminent.
Patent Literature 1 and 2 have disclosed such a diagnostic method and a diagnostic apparatus for diagnosing an electrochemical sensor.
Patent Literature 1 provides a method for applying a pulse voltage between the sensing electrode and the opposite electrode of an electrochemical sensor, and diagnosing whether or not the electrochemical sensor is accurate on the basis of an output of the electrochemical sensor after the pulse stops; namely, the capacitance output (discharge characteristic). Specifically, it is held that an error such as the electrochemical sensor malfunctioning can be diagnosed by comparing the capacitance output when functioning correctly to the actual measured capacitance output.
Patent Literature 2 provides a method for diagnosing that an error such as a short between the sensing electrode and the opposite electrode of an electrochemical sensor or a reduction in sensor sensitivity has occurred on the basis of whether the output of the electrochemical sensor is a peak output or a bottom output when turned on again after turning off the power source of a gas detector incorporating the electrochemical sensor.    [Patent Document 1] JP (Kokai) 2000-146908    [Patent Document 2] JP (Kokai) 2004-279293